1. Field of the Invention
The present invention relates generally to a magnetic recording and regenerating unit for photographic film and a camera, and more particularly to a magnetic recording and regenerating unit which records magnetic information in a magnetic recording layer on the photographic film and regenerates the magnetic information recorded in the magnetic recording layer, and a camera which the magnetic recording and regenerating unit applies to.
2. Description of Related Art
Advanced photographic film has been proposed in which one side of silver salt film is coated with a magnetic layer (U.S. Pat. No. 5,130,745). A film cartridge which contains the film and a camera which uses the film cartridge for photographing have also been proposed, and they are standardized worldwide.
As shown in FIGS. 32(a) and (b), an advanced cartridge roll film 100 is constructed in such a manner that the film 103 which is wound around a spool 102 is stored in a cartridge case 101, which is substantially cylindrical. A light-shielding lid 104 is provided at one end of the cartridge case 101. The film 103 is completely stored in the cartridge case 101 when the roll film 100 has not loaded in the camera or after the roll film 100 has been taken out from the camera, and the light-shielding lid 104 protects the film 103 from external light.
A data disk 105 is provided at a side end of the cartridge case 101, and the data disk 105 rotates in association with the spool 102. A bar code is printed on the exterior face of the data disk 105, and the bar code indicates the type and sensitivity of the film 103, the number of frames to be exposed, etc.
Apertures which are shaped like a circle, a square, a cross and a semicircle are formed on the other side end of the cartridge case 101. A sectorial white plate (not shown) is provided at the back of these apertures, and the white plate rotates in association with the spool 102. One of the circle, the square, the cross and the semicircle is displayed in white according to a position where the white plate stops. The display of the circle in white indicates that the film in the cartridge case 101 is unexposed; the display of the square in white indicates that the film has already been developed; the display of the cross indicates that the film has already been exposed but undeveloped; and the display of the semicircle in white indicates that the film has some unexposed frames remaining. The display in white is called VEI (visual exposure index), and the index is seen with eyes from the outside to confirm the status of the film used.
The film 103 is constructed in such a way that a surface 103F of the film base is coated with a silver salt photosensitive layer and the reverse side 103R of the film is coated with a magnetic recording layer. Multiple perforations 121 are formed at the edge of the film 103 to specify the range of each frame 120. The photographing information such as the type of a light source for photographing and a focal length, and the information such as the title of the photograph used as a message to a user can be magnetically recorded in magnetic record areas 124, 125 at the upper and lower end of each frame.
When the cartridge film is loaded in the camera, an optical reading mechanism in the camera reads information indicated with the bar code on the data disk 105, and detects the position of the white plate, thereby automatically recognizing the information relating to the film and the used status of the film. In the case of the cartridge film with no exposed film or with some unexposed frame remaining, the light-shielding lid 104 is opened and the spool 102 is rotated in a predetermined direction, so that the film 103 can feed to the first unexposed frame.
After all frames on the film 103 are exposed, a rewind mechanism in the camera takes up the film 103 into the cartridge case 101, and closes the light-shielding lid 104. Further, the white plate, which is fixed on the spool 102, is stopped in a manner to face the cross-shaped aperture, thereby displaying the cross in white to indicate that the film has already been exposed.
If the film is forcibly rewound during photographing with some unexposed frames remaining, the rewind mechanism in the camera takes up the film 103 into the cartridge case 101, and closes the light-shielding lid 104. Further, the white plate, which is fixed on the spool 102, is stopped in a manner to face the semicircular aperture, thereby displaying the semicircle in white to indicate that the film has some unexposed frames remaining.
On the other hand, if the loaded cartridge contains the film on which all frames are exposed or developed, the process is executed to prevent the automatic feeding or the like because photographing is impossible.
According to the above-described camera, the film may be forcibly rewound in a state where there are some unexposed frames remaining on the film, and the film cartridge may be taken out of the camera (hereinafter this film cartridge, which contains the film being partially exposed, is referred to as "a partial cartridge"). When the partial cartridge, which contains the photographic film with one or more of exposed frames and one or more of unexposed frames, is loaded again in the camera, the information in the magnetic recording layer is read via a magnetic head in the camera, and the film feeds to an area with no magnetic information recorded. Thereby, the photographing can be performed from an unexposed frame.
The magnetic recording layer formed on the photographic film has a low magnetic density. Moreover, the base thereof is harder than a conventional magnetic tape, and thus a head touch easily becomes unstable. Hence, a special magnetic head only for reading is provided in which the number of turns of the coil is increased so as to exactly read the information.
In a magnetic head (a regenerating head) in a conventional magnetic regenerating unit for a camera, which regenerates the magnetic information from the magnetic recording layer on the photographic film, the number of turns of the coil wound around the core is approximately 1500. That is because S/N is lowered if the number of turns is small, and thus the magnetic information is difficult to read.
On the other hand, a magnetic head (a recording head) which records the magnetic information in the magnetic recording layer on the photographic film cannot be driven if the number of turns is large. For this reason, the number of turns of the coil is usually between 80 and 100. Thus, a regenerating head and a recording head are provided independently of one another, or a recording coil and a regenerating coil are wound around a core.
FIG. 33 illustrates an example of a conventional magnetic head driver. The magnetic head driver 150 is driven by electricity supplied from a power source V.sub.B, and a lithium battery, which is used as a power source for the camera as a whole, is used as the power source V.sub.B. A magnetic head 152 is driven by bridge-connected switching transistors 154, 155, 156, 157, and ON/OFF of which are controlled by control transistors 160, 161. The control transistors 160, 161 are turned on and off, respectively, by switching signals (a clock pulse and a data pulse) which oppositely switch the first port P1 and the second port P2 onto a high (H) level and a low (L) level.
After the start of the magnetic recording, if the port P1 becomes the L level and the port P2 becomes the H level according to the clock pulse and the data pulse from a microcomputer, the control transistor 160 is turned off and the control transistor 161 is turned on. Thereby, the switching transistors 154, 156 are turned off, and the switching transistors 155, 157 are turned on. Thus, the recording current I.sub.H flows from the right to the left in the drawing through a coil 152a, which composes the magnetic head 152. Thereby, the magnetic head 152 generates a magnetic field in which the magnetic flux turns in the film feed direction, and a magnetized area ("N magnetized area") in which the magnetic flux turns in the film feed direction is recorded in the magnetic recording layer. On the other hand, when the port P1 becomes the H level and the port P2 becomes the L level, the control transistor 160 is turned on and the control transistor 161 is turned off. Thereby, the switching transistors 154, 156 are turned on, and the switching transistors 155, 157 are turned off. The recording current flows through the coil 152a in the reverse direction, and the magnetic head 152 generates a magnetic field such that the magnetic flux turns in a direction opposite to the film feed direction, and a magnetized area ("S magnetized area") in which the magnetic flux is turns in the direction opposite to the film feed direction is recorded in the magnetic recording layer.
The above-described conventional magnetic recording and regenerating unit, however, employs a sensitive and precise regenerating magnetic head in order to read the information recorded in the magnetic recording layer, and this magnetic head is large and expensive. Moreover, since the regenerating magnetic head is provided independently of the recording magnetic head, or the recording and regenerating head uses two coils wound on a core for recording and regenerating, the magnetic head(s) is large and a driver circuit, etc. connected to the magnetic head has the complicated structure. For this reason, the cost is increased, and the camera cannot be compact and lightweight. Since the number of turns of the coil is large, the magnetic head (the regenerating head) in the conventional magnetic regenerating unit for the camera is large and expensive. Due to the difference in the number of turns of the coil in the recording head and the regenerating head, it is impossible to combine them as one magnetic head.
Furthermore, the above-mentioned magnetic head reads the magnetic information while the film is feeding, and thus the noise of the film feed motor easily overlaps with the information. In particular, since the recently-developed cameras are required to be compact, and the motor is arranged close to the magnetic head, the errors easily take place in the process of reading the magnetic information.
If the conventional magnetic head driver is used as shown in FIG. 33, and when all the switching transistors 154, 155, 156, 157 are turned off on completion of recording the last "S magnetized area", a closed circuit including the magnetic head 152 becomes unstable, and an oscillating current flows through the coil 152a due to the effects of inductance and capacitance within the magnetic head driver. For this reason, there is a problem in that the improper magnetic information is recorded after recording of the last "S magnetized area" because of the oscillating current. To solve this problem, a method has been proposed in which all the transistors 154, 155, 156, 157 are turned on to short-circuit the coil 152a after recording of the last magnetic data (Japanese Patent Application No. 7-128234). This method is effective in a magnetic head driver only for recording, which can have high resistance 164, 165, but is not suitable for a magnetic head driver which is used for both recording and regenerating and has to have small resistance 164, 165 because of the small number of turns of the coil 152a.
On the other hand, there are well known a four-terminal magnetic head in which the recording coil and the regenerating coil are wound on a core, a three-terminal magnetic head in which the regenerating coil includes the recording coil, and the like. In the magnetic head which is constructed in this manner, the number of turns of the regenerating coil is usually dozens of times as many as the recording coil. When the recording current flows through the recording coil with the drive power of approximately 3 V, a induced current flows through the regenerating coil and a high induced voltage of several dozens V is generated between the ends of the regenerating coil. If the high voltage is directly applied to the amplification circuit for regeneration, elements composing the amplification circuit such as an operational amplifier are broken.
If a protection circuit is provided at the input stage of the amplification circuit for regeneration, or a switch, etc. for electrically cutting off the regenerating amplification circuit from the magnetic head is provided in order to eliminate the above-described disadvantages, the great noise overlaps with the regenerated signal, and the cost is increased.
Furthermore, if the partial cartridge is loaded in the camera, whether a frame is exposed or unexposed must be determined, and the photographic film must be fed to the first unexposed frame, thus requiring much electricity to prepare for photographing. In particular, if whether a frame is exposed or unexposed is determined according to the magnetic information recorded in the magnetic recording layer on the photographic film, the photographic film must be fed at a proper speed. If, for example, the film feed speed changes due to the exhaustion of the battery in the camera, whether a frame is exposed or unexposed cannot be determined, and thus it is impossible to prepare for photographing of the partial cartridge.